Alexander and Louis-Dreyfus have made multiple guest appearances on "Curb," which stars "Seinfeld" co-creator Larry David as a fictional version of himself, and Seinfeld had a brief cameo in 2004. The coming episodes, however, will mark the first time all four cast members have reunited on a scripted (or semi-scripted) show since "Seinfeld" ended in 1998.

The cast did come together for an NBC special, "The Seinfeld Story," in 2004 that coincided with the release of the show's first few seasons on DVD. Seinfeld is also executive producing an unscripted series called "The Marriage Ref" for NBC, though he's not expected to appear on camera.

"Curb Your Enthusiasm" last aired in November 2007. There's no exact timetable for the show's return to HBO, but new episodes are expected to start airing later this year.